Flat panel displays incorporating touch screen features usually employ either capacitive or resistive detection mechanisms. A typical resistive touch screen thin-film transistor liquid crystal display (TFT LCD) employs a flexible conductive membrane and a moderately conductive substrate placed over the TFT LCD panel to detect objects physically touching the front of the display. When an object deforms the membrane enough to contact the underlying substrate a controller determines the position of the resulting contact by measuring the resistance between that contact point and the edges of the underlying substrate. By contrast, a typical capacitive touch screen TFT LCD uses a series of materials including a thin transparent conductive layer (e.g., Indium Tin Oxide (ITO)) overlaying the display panel to detect the capacitive coupling resulting from objects placed in proximity to the conductive layer.
Traditional resistive touch screen displays are mechanically complex and require physical pressure to detect objects. Both techniques add a significant number of relatively complex steps to the manufacturing process and tend to reduce the resulting display's optical performance. In addition, standard approaches to both technologies produce displays that require added calibration and testing in the post-manufacturing production process and the resulting displays are typically less robust then similar non-touch screen displays. Further, neither standard resistive nor standard capacitive touch screen displays are capable of sensing multiple touching or proximity events simultaneously.